Isolation Transformer

Looking for a 5kVA isolation transformer to go from an ungrounded 480VAC 3ph. source to a 480VAC 3ph. Wye w/ a center ground.

Mostly what I've found are called "drive isolation transformers" and are way overkill according to the manufacturer of the device I'm powering. They start at 7.5 kVA and are built to take 200% current draw for 1 hr. They are also close to $1000.00

The device I'm powering is a servo drive and can draw 6A continuous or 12A peak but only for a few seconds.

Is anything like this available off the shelf?

Thanks,

How about a line reactor? All of the drives vendors offer them, primarily for harmonic suppression. They are significantly less expensive than "Drive Isolation Transformers" and they come in sizes smaller than 7.5 KVA.

I haven't been able to get a definitive word on whether or not the line reactor will work

BUT...

From what I have seen, the reactor is a serial type device... all the current flows through the device. If the power source starts out ungrounded then the line reactor can't change that as far as I can tell.

The servo drive I'm working with specifically need 480 VAC 3Ph. Wye with a center tap ground. I don't think the reactor can change an ungrounded Delta to a grounded Wye.

Are you searching for 3 phase transformers? Check for single phase, buy 3, and build your own. Also, don't limit yourself to "isolation". Look for standard transformers that can be wired as isolation. A 480 to 240 with 2 output windings may be easier to get and cheaper.

Try Using A Resistor Grid To Give The Desired Effect, Sometimes Referred To As A Wheatstone Bridge.

Why do you want to go from 480V to 480Y/277?

If your equipment requires a neutral or a maximum of 277V to ground, you have no choice you must use a transformer, however it rarely needs to be a drive type.

If you are looking to protect your servo from the power grid (i.e. reduce the fault current) you may be able to use a line side reactor.

If you are trying to protect the power grid from your servo (i.e. ground faults caused by misfiring of SCRs) you will probably need a drive isolation transformer.

Be clear on what you are trying to accomplish, before trying to select equipment.

You need a drive isolation transformer to do what you mention. You could conceivably get the job done with three small single phase 480/277V transformers but where would you find those?!!

Don't pay extra for electrostatic shielding etc etc in the drive isolation transformer. Just a basic one will do.

Yes, the transformer is expensive but that is part of the price for choosing an ungrounded power supply. They look cheaper on the front end but........surprise, they aren't necessarily in the long run. And, in my opinion, the floaters carry hazards to personnel which are rarely addressed responsibly by specifying engineers.

Probably ought to stop with that.

Ah, chosing the power source... Never have got to do that myself.

Usually done by someone years and years ago when the electrical service was set up. I have customers with almost every conceivable type of power set up imaginable.

However, this customer has used a servo drive in the past from another manufacturer that tolerated an ungrounded source... even had a jumper for it (not sure if it was safe but it was in the manual ).

I guess in the long run it's a better system with the transformer, he just wasn't expecting the cost of it. Maybe he should have read the manual before he bought it ... but I should have brought it up also...

Don't pay extra for electrostatic shielding etc etc in the drive isolation transformer. Just a basic one will do.

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Again, any suggestions for sources of a "basic" 5kVa 3 phase isolation transformer would be appreciated.

Acme Transformer

DickDV said:

Acme Transformer

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I will second that.

You can get just about any type of transformer from them.

I have used 3 480 primary and dual 240 center tapped transformers to get 480 3 phase secondary and connected WYE to get the ground/common to a drive.

You should be able to get a 480/480 delta/wye transformer from ACME's catalog.